Silicon-On-Insulator (SOI) based technology allows a micro-electronic or Micro-Electro-Mechanical (MEMs) device to be fabricated in a silicon layer that is located above an insulating layer (e.g. a buried oxide layer). The insulating layer is located over a silicon substrate. Electronic devices, such as a transistor as well as MEMs type devices are fabricated in the layer of silicon located on top of the insulating layer. This technique may provide higher speeds and use less power by reducing capacitance, reducing or eliminating the reverse leakage of the p-n junctions and thus making device operation in SOI superior to devices fabricated in conventional Complementary Metal-Oxide Semiconductor (CMOS) bulk silicon based processing.
One type of structure that may be implemented in SOI is a pressure sensor. Pressure sensors include a piezo-resistor coupled with a diaphragm. The piezo-resistor is embedded in the diaphragm, and responds to a change in stress of the diaphragm with a change in resistance as a consequence of the piezo-resistive effect. When the pressure applied to the diaphragm changes, the amount of deflection of the diaphragm changes accordingly, which results in a change in the stress level in the silicon diaphragm. This in turn causes the piezo-resistor element to increase or decrease in resistance. Thus, the increase or decrease in resistance may be used to gauge the amount of pressure being applied to the diaphragm.
In present piezo-resistive based pressure sensors, a voltage or current source is coupled to the piezo-resistor via a leadout resistance. Unfortunately, this leadout resistance decreases the sensitivity of the pressure sensor by increasing the overall resistance of the pressure sensor. A current or voltage signal applied to the piezo-resistor must also be applied the leadout resistance. Because the leadout resistance is in series with the piezo-resistor, a portion of the current or voltage signal is distributed across the leadout resistance. The larger the leadout resistance, the larger the portion of the signal distributed across the leadout resistance. Current processes do not provide a means to tailor the thickness of the piezo-resistor independently of the leadout resistor such that the leadout portion of the overall resistance of the pressure sensor is adjustable in relation to the resistance of the piezo-resistor, thereby allowing the sensitivity of the pressure sensor to be increased or decreased without degrading the overall performance of the sensor.
The techniques and structures disclosed herein are believed to improve upon these prior attempts.